C.2.18 Particle system changes

The PARTICLES mesh object have been rewritten.

iParticlesStateBase, iParticlesObjectState,
iParticlesFactoryState and iParticlesPhysics have been removed
in favour of the new iParticleSystemBase, iParticleSystemFactory
and iParticleSystem.
Particle emission is controlled via instances of iParticleEmitter,
physical effects controlled via iParticleEffector.